OBJECTIVES: To assess the ability of risk of malignancy index (RMI) 1 to discriminate between benign and malignant pelvic masses. METHODS: Between January 2007 and December 2010, 547 women with pelvic masses were evaluated. Their medical records are reviewed here retrospectively. The sensitivity, specificity and positive and negative predictive values of the cancer antigen (CA) 125 level, ultrasound findings and menopausal status in the prediction of malignant pelvic masses were calculated and compared individually or combined using the RMI 1. RESULTS: The receiver operating characteristic (ROC) curves of CA 125, the ultrasound score and the RMI 1 were all found to be relevant predictors of malignancy. ROC analysis of the RMI 1, CA 125 serum levels, ultrasound score and menopausal status showed areas under the curves of 0.795, 0.782, 0.784 and 0.594, respectively. The RMI 1 was found to be statistically significantly correlated with menopausal status (P = 0.001), while not statistically significantly correlated with CA 125 (P = 0.628) or the ultrasound score (P = 0.541). The RMI 1 at a cut-off of 150 - with a sensitivity of 77.9%, specificity of 81.1%, positive predictive value of 51.7% and negative predictive value of 93.4% - showed the highest performance in determining the malignant tendency of pelvic masses. CONCLUSION: Accepting a RMI 1 cut-off value of 150 results in statistically more significant diagnostic criteria than menopausal status for the discrimination of benign and malignant pelvic masses.